chapter 16

According to the crystal structure, the lac repressor binds to ______ lac operator site(s) at a time.

2

In the trpL mRNA, the number of stem-loops that are possible is

3

Studies indicate that the lac operon has ______ operator site(s) for the lac repressor.

3

In the trpL gene, which stem-loop, together with the U-rich attenuator sequence, acts as an intrinsic terminator?

3-4

The lac repressor is composed of how many identical subunits?

4

Why is a merozygote better at complementing a mutation in a trans-acting factor than in a cis-acting element?`

A cis-acting element must be adjacent to the gene it is regulating.

What effect would a loss-of-function mutation in the lacI gene and a mutation in operator that prevents repressor binding have?

Both result in constitutive expression of the lac operon.

When tryptophan levels in the cell are low, the trp repressor ____________ bind to the operator site. RNA polymerase ____________ transcribe the trp operon

Cannot; Can

Monod, Jacob, and Pardee learned about the lac operon using bacterial strains called merozygotes. Since lacI encodes a diffusible protein, in a merozygote, the gene on the__ ____could supply the mutant cell with functional repressor protein.

F factor

The ______ gene encodes a repressor protein.

LacI

Can a particular segment of mRNA from the trp operon participate in the formation of more than one stem loop at the same time?

NO

When the lac repressor binds to the lac ----- site, RNA polymerase cannot transcribe the lacZ, lacY or lacA genes.

O

β-galactosidase activity can be detected using the lactose analog β-------_ because β-glalactosidase cleaves it to a product with a yellow color.

ONPG

How does the product of the micF gene regulate the expression of the ompF gene?

The binding of the micF RNA prevents translation of the ompF mRNA.

How does an effector molecule influence gene expression?

The effector molecule binds to a regulatory protein and affects its ability to bind DNA.

Why is transcription of the lac operon low when both lactose and glucose are present?

The low levels of cAMP result in CAP not binding to the CAP site.

An operon is a group of two or more genes under the transcriptional control of ______.

a single promoter

A regulatory protein that increases the rate of transcription is a(n)

activator

The observation that a particular enzyme appears within a cell only after a cell has been exposed to the enzyme's substrate is called enzyme

adatation

Cyclic-AMP is a small effector molecule produced by the enzyme

adenylyl cyclase

Constitutive genes encode proteins that the cell needs ______.

all the time

The small effector molecule that prevents the lac repressor from binding to the operator site is

allolactose

In postranslational regulation, the final product of a metabolic pathway may bind to the---------site of an enzyme and inhibit its catalytic ability.

allosteric

An enzyme may contain two sites: a catalytic site, and a regulatory or

allosteric site

In the absence of lactose, the lac repressor ______.

allows very small amounts of lac operon enzymes to be made

The binding of a small effector molecule to a regulatory protein alters the regulatory protein's conformation, and that ______.

alters the protein's ability to bind to DNA

The RNA transcribed from the micF gene is complementary to the ompF mRNA and acts as a(n)

antisense strand

Unregulated genes are also called

constitutive genes

Posttranslational regulation refers to ______.

control of proteins already in the cell

For the trp operon, tryptophan acts as a(n) ______.

corepressor

The product of the biosynthetic activities of the enzymes from an operon may act as a(n)------_ if the operon is repressible.

corepressor

Many bacterial species use sugars sequentially. This is called ______.

diauxic growth

The normal lacI gene on the F' factor could rescue the lacI- mutants because the product of the lacI gene encodes a ______.

diffusible protein

Examples of a(n) ---------stress that might require a bacterium to produce a specific protein include osmotic shock or heat shock.

environmental

The genes in the trp operon encode ______.

enzymes used in tryptophan biosynthesis

The enzyme beta-galactosidase cleaves the sugar lactose into ___ and ___

glucose and galactose

The transport of ______ into a cell causes a(n) _______ in the concentration of cyclic-AMP by inhibiting adenylate cyclase.

glucose; decrease

When both lactose and glucose are absent from bacterial cells, concentrations of cAMP are ______.

high

When tryptophan levels in the cell are---------_, translation of the trpL mRNA continues to its stop codon, which terminates further transcription of the operon.

high

Monod and Jacob studied ____ metabolism in E. coli.

lactose

A protein such as a repressor that inhibits transcription is exerting

negative control of transcription

A loss-of-function mutation in a gene encoding a repressor protein has the same effect as a mutation in the ______.

operator site

The research of Jacob and Monod provided ______.

our initial understanding of gene regulation

Transcription regulation by an activator protein is considered to be ______ control.

positive

In bacteria, the most common way to regulate gene expression is by influencing the ______.

rate of transcription initiation

a corepressor is a small molecule that binds to a ______ protein, thereby causing the protein to bind to the DNA, while an inhibitor binds to an______ protein and prevents it from binding to the DNA

repressor and activator

The CAP site and the operator site are ______ that function in gene regulation.

short DNA segments

Which of the following can be regulated by riboswitches?

splicing transcription translation RNA stability

A translational repressor protein may bind to the mRNA and ______.

stabilize a secondary structure that prevents translation

The mRNA from the trpL gene has four regions that are complementary to each other and cause the mRNA to form

stem loops

When attenuation occurs in the trp operon, the mRNA is ______.

terminated before transcription of the genes required for tryptophan biosynthesis

The mRNA made form the trpL gene contains codons for 14 amino acids that form

the trp leader peptide

When four molecules of allolactose are bound to the lac repressor, the lac operon is induced, and RNA polymerase ______.

transcribes the structural genes of the operon

Riboswitches can regulate ______.

transcription or translation

If a riboswitch controls access to the Shine-Dalgarno sequence, which of the following will be regulated?

translation

The TPP riboswitch in E. coli controls -----_, whereas the TPP riboswitch in B. subtilis controls-----

translation; transcription

When attenuation occurs, the mRNA from the trp operon is made as a short piece that terminates shortly past the ______ gene.

trpL

The lac repressor does not completely inhibit transcription of the lacZ, lacY, and lacA genes.

true

In the E. coli thiMD operon, the 5' end of the mRNA folds into a structure with a stem-loop called the Shine-Dalgarno-------that keeps the Shine-Dalgarno sequence accessible to the ribosome.

antisequestor

In the thi operon in B. subtilis, when levels of TPP are low, the 5' end of the mRNA forms a stem-loop structure called a(n)------_ that allows transcription to continue.

antiterminator

Riboswitches may be found in

bacteria, archaea, fungi, and plants.

The small effector molecule produced by the enzyme adenylyl cyclase is ______.

cAMP

When the lac repressor is bound to the operator, RNA polymerase ______ the lacZ, lacY, or lacA genes.

cannot transcibe

Inducible operons usually encode ______ enzymes, and repressible operons usually encode ______ enzymes.

catabolic; anabolic

The somewhat imprecise term that describes how transcriptional regulation is influenced by glucose is

catabolite repression

In the thi operon in B. subtilis, when levels of TPP are high, the mRNA folds into a stem-loop structure that ______.

causes attenuation

Select the processes that are regulated at the genetic level.

cell division metabolism response to the environment

The mRNA made from the trpL gene has four regions that can ______.

form stem loops

The lacA gene encodes the enzyme

galactoside transacetylase

Genes that are regulated by inducers are called

inducible genes

In feedback inhibition, the final product in a metabolic pathway ______.

inhibits an enzyme that acts early in the pathway

When translation is regulated genetically, which phase of translation is usually blocked?

initiation

In attenuation, transcription ______.

is stopped prematurely

The three protein-encoding genes in the lac operon are

lacZ, lacY, and lacA

The exposure of bacterial cells to---------increases the levels of lactose-utilizing enzymes 100- to 10,000-fold.

lactose

The lacA gene encodes galactoside transacetylase, an enzyme that covalently modifies ______.

lactose

When only ______ is present in bacterial cells, cAMP levels are high.

lactose

For the lac repressor tetramer to bind two operator sites, a(n)----must form in the DNA

loop

When both lactose and glucose are present, transcription of the lac operon is ______.

low

A translational repressor protein binds to ______.

mRNA near the start codon

When TPP levels are low, the mRNA of the E. coli thiMD operon forms a stem-loop structure that ______.

makes the Shine-Dalgarno sequence available to the ribosome

Genes that are regulated by corepressors or inhibitors are called

repressible genes

A regulatory protein that binds to DNA and inhibits transcription is called a(n)

repressor

The conversion of a riboswitch form one conformation to another is due to ______.

the binding of a small molecule

The corepressor for a repressible operon may be ______.

the product of the biosynthetic activities of the operon's enzymes

A DNA segment that must be adjacent to the gene(s) it regulates is a

cis acting element

Unregulated genes have ______.

constant levels of expression

The trp operon is regulated by a repressor protein and by -----------in which transcription is stopped prematurely.

attenuation

Regulation of the trp operon involves the process of--------_, in which transcription begins but terminates before the entire mRNA is made.

attenuation

The enzyme β-galactosidase is encoded by which gene?

lacZ

An operon encodes an_____ mRNA, an RNA that contains the sequences of two or more genes.

polycistronic